This invention relates to a process for recovering nickel from spent electroless nickel plating solutions so as to permit safe disposition of such spent solutions.
Electroless nickel plating solutions are well known for use in plating nickel on to various substrates. Such solutions have relatively short lives and must frequently be discarded into waste disposal systems. The limits set by authorities for such nickel disposition are constantly being restricted such that removal of the vast majority of the nickel prior to disposition of spent solutions, as an effluent, is required.
There has been described in U.S. Pat. No. 4,144,149, entitled "Method for Working Up Aqueous Residues From Metallizing Baths", issued Mar. 13, 1979, a process for puifying electroless copper metalizing baths containing an amino compound, such as ethylenediaminetetraacetic acid (EDTA) where the bath is adjusted to a pH of 10-12 using sodium hydroxide or other inorganic base, and electrolyzing the basic solution using steel sheets as cathodes and platinum-coated titanium sheets as anodes. In that reference, after passage of a current for a period of time, the metal is separated, the solution acidified, and further electrolysis carried out on the acidified bath to eliminate the complexing ability of the amino compound. That reference is specific, however, to aqueous baths containing at least one organic amino compound such as EDTA or other organic amino complexing agent.
While some chemical methods have been proposed for removal of nickel from spent solutions, such methods are relatively inefficient, expensive, and often result in volumes of sludge which must then be further treated or taken to landfill systems.
It was believed by many that nickel could not be plated out of such spent solutions, and thus no effective means for removing nickel from such solutions prior to discharge as effluent was provided.
I have found, however, that by following specific process steps, according to the present invention, nickel can be effectively electrolyzed out of spent electroless nickel containing solutions both efficiently and inexpensively.